This invention relates to a mount used for connecting two members while isolating and/or controlling the transfer of motion, and particularly motion due to vibration, between these members. Mounts of the general type are described in U.S. Pat. Nos. 3,147,964; 3,508,745; 3,642,268; and 3,698,703.
The earlier type of mount disclosed in said U.S. Pat. No. 3,147,964, utilizes primarily the directed energy absorbing characteristics of a compressed rubber bushing to control the transmission of vibration between two members, and also to provide a certain mount of shock isolation in the mounting of one mechanical member to another, while still mechanically connecting the members as desired. These members can be any of a vast variety of devices such as different parts of mechanisms or vehicles, supports for machinery, and packaging supports for large masses. Of particular interest are the connections of chassis and body parts in vehicles. For example, the mounting of an engine in an automobile requires control and isolation in six different degrees of freedom, namely motion along X, Y and Z axes and rotation about these axes, namely roll, pitch and yaw. In this area of application alone, the modern demands for vibration control isolation and adequate support and anchoring present sophisticated mount design requirements which are aggravated by the need to accomodate some degree of misalignment which is to be expected in mass production systems.
The aforementioned '268 and '703 patents disclose such mounts wherein the vibration isolating effect of a resilient (such as rubber) member coupled between the members is modified by the placement of a damping liquid in cavities located on opposite sides of and within the resilient member. These cavities are connected through a passage which limits the flow of the liquid between the cavities, thus further damping the motion of the resilient member along a plane extending through the two cavities. Details of the hydraulic damping conditions are disclosed particularly in the '268 patent, wherein it is stated that "various dynamic rates of the bushing can be readily controlled through the judicious selection of a properly sized orifice between the pockets" and, in reference to an embodiment with an internally tapered tube inserted in the connecting passage, this "type of tube would give damping characteristics similar to a corresponding tube having a uniform diameter corresponding to the minimum diameter of" the modified tube. Thus it appears that these prior art patents teach the important parameter is the friction effect of the liquid, and adjusting damping action is accomplished by the proper selection of the diameter, or cross-sectional area, of the connecting passage between the liquid filled cavities.
Also with respect to such prior art fluid damped mounts, the metal to rubber bonds in those devices described are of the post-bonded type, which means that the bond is form by assembling separate rubber and metal parts, with an adhesive therebetween which is later thermally activated to provide a bond between these parts. Various types of such bonding are discussed in those patents. In many applications of mounts such a bond is not reliable from a physical adhesion standpoint, and may also have discontinuities which alter the desired continuous metal-rubber bond that is needed.
It is generally recognized in the art that a good bond between the metal and rubber parts in such mounts introduces an impedance mis-match into the mechanical system which is effective in minimizing the transmission of vibrational energy across this bond. Each such interface in the path along which vibrational energy can be directed will substantially damp the vibration and provide additional isolating capacity. Thus, it is also desirable to maximize the use of such interfaces as possible without compromising the over-all mechanical design of a mount.